The great thing about “The Simpsons” is the freedom to stop watching for, oh, three or four years and return to find everything exactly where you left it.

The great thing about “The Simpsons” is the freedom to stop watching for, oh, three or four years and return to find everything exactly where you left it. The latest annual Halloween-themed episode opens with a fabulous (and already widely circulated) election-eve gag about rigged voting, but that’s just the tip of an irreverent, at-times surreal iceberg that parodies “Transformers,” the “Peanuts” specials and AMC’s “Mad Men,” while finding time to question Abe Lincoln’s sexuality. There happily remain no sacred cows (or even lipsticked pigs) in “Simpsons”-land — which is no mean feat 20-some-odd years later.

Clever as it is, the bit in which Homer tries to vote for Barack Obama — only to have the machine keep ringing up ballots for “President John McCain” — amounts to a throwaway prior to the three “Treehouse” segments: Transformer-like robots laying waste to Springfield; Homer being recruited to murder celebrities so that advertisers can brazenly exploit their likenesses; and a “Great Pumpkin” tribute, complete with (in the show’s single best gag) a nod to why those Charlie Brown parents always sounded like a muted trumpet.

As has always been the case, most of the material in the middle sending up deceased luminaries like John Wayne and Edward G. Robinson will fly over the heads of children and goes directly toward their parents — most of whom were kids, notably, back when the show premiered during the first Bush administration. Seldom has a series benefited more from relying upon the writers’ instincts that if the jokes are funny to them, that will somehow connect with an audience.

Admittedly, the series has a way of quickly degenerating from satirical into silly, in a less-exaggerated version of the excesses to which “South Park” often falls prey. That occurs in a few places here, especially as the episode’s mutilated bodies (amazing what you can get away with in animation) begin to pile up.

For the most part, though, this latest “Treehouse” is another reminder that “The Simpsons” has managed to stay remarkably fresh, if not as ageless as its animated stars — and thus worthy of the epic, Super Bowl-like Roman numeral designation that “XIX” denotes.